For thin stuff just score and snap. You can actually get utility knife blades for this purpose. Essentially they're regular utility blades except they aren't sharpened, just a dull square edge. They work pretty well. Just make sure when you score it you score it deep enough, at least 1/3 of the thickness, otherwise you might get an uneven break.
For thicker stuff, anymore we just have it laser-cut, easier and much cleaner.